Explosive centerhole anchor



Sept- 17 1968 E. w. PARSONS ET Al.

EXPLOSIVE CENTERHOLE ANCHOR (5 Sheets-Sheet l Filed May 2, 1966 /NVE/VTOHS Edward w. Parsons Lars Osen ATTORNEYS V NN\ 9% m\ l Mw E. W. PARSONS ET AL ExPLosIvE CENTERHOLE ANCHOR Sept. 17, v1968 3 Sheets-Sheet '2 Filed May 2. 1966 INVENTORS Edward W. Parsons Lars Osen ATTORNEYS WMM E. w. PARSONS ET AL 3,401,461

EXPLOSIVE CBNTERHOLE ANCHOR Sept. 17, 1968 3 Sheets-Sheet 5 Filed May 2, 1966 INVENTORS Edward W. Parsons Lars Ose ATTORNEYS www United States Patent O 3,401,461 EXPLOSIVE CENTERHOLE ANCHOR Edward W. Parsons and Lars Osen, Spokane, Wash., as-

signors to the United States of America as represented by the Secretary of the Interior Filed May 2, 1966, Ser. No. 547,044

5 Claims. (Cl. 33-125) ABSTRACT OF THE DISCLOSURE This invention relates to improvements in ground anchors and more specifically to improvements in drillhole anchors designed for use in a system of measuring ground movements between points along .a drillhole.

U.S. Patent 3,327,396 describes such a system for measuring ground movements, wherein a hole is drilled int-o the earth at the desired location for testing and from one up to ten anchors are inserted into the drillhole at a predetermined depth and securely fastened to the wall of the drillhole. Metal wires, attached to each of the anchors, extend to the surface or collar of the hole where they are connected to a meter which monitors the movement of each wire and indicates movement of rock at or around the various anchors.

Previous to this invention, no satisfactory centerhole anchor for multiple-point tensioned-wire connections lbetween anchors in a long drillhole had been known. Anchors using a threaded device, similar to that described in U.S. Patent 2,661,649, for expanding contact prongs on the anchor have been used, 4but the twisting action required to secure such an anchor often gives rise to rotation of the whole anchor causing the tensioned wire from that anchor to come into contact and become entangled with tensioned wires emanating from previously installed anchors. No sure method is known for straightening twisted wires many feet within a long drillhole. Connecting tensioned wires twisted together render the installation useless.

Briefly, the present invention comprises an anchoring arrangement for placing an immovable double-walled sleeve at a predetermined depth within a drillhole. The anchor is secured within the hole by remotely detonating an explosive charge contained within the anchor. The `anchoring arrangement may consist of a plurality of anchors in series within the drillhole. Furthermore, the

anchors are designed so that tensioned wires are connected to the anchors and run to the opening of the hole, and so that tensioned connecting wires from anchors 4deep Within the hole pass unobstructed through the centerholes of shallower anchors.

The anchoring arrangementof the present invention may ladvantageously be used to secure an immovable point in a hole or shaft deep within a solid with greater ease than heretofore possible with the devices of the prior art. Furthermore, the present anchor used in the arrangement may be designed specifically for use in a particular solid. Thus a degree of adherence is obtainable with the present ,anchor which has not been possible with other known devices. The anchor of this invention may be used to particular advantage to extend the capabilities of systems used in measuring and studying the movements in earth rice formations in the vicinity of various excavations such as mine stopes and shafts as well ,as movements associated with blasting and rockbursts. The present anchor may be easily placed at any desired depth within ra drillhole and moreover does not require a twisting action to install, which could impede or restrain free movement of the c011- necting wires between other anchors in the drillhole and an instrument panel at the collar of the hole. Furthermore, the present anchor provides an adherence not obtainable with previous devices thus guaranteeing creep-free operation for the duration of the measuring period and allowing use of higher tensions in the connecting wires.

Accordingly, it is an object of this invention to provide an anchoring arrangement which contains an improved centerhole anchor.

Further, it is an object of this invention to provide an anchoring arrangement containing an improved centerhole anchor which does not require a mechanical action to be set in place.

Further, it is an object of this invention to provide an anchoring arrangement which contains a centerhole ,anchor which may ybe used to connect tensioned wires from points within a drillhole to a point at the opening to a hole.

f Further, it is an object of this invention to provide an anchoring arrangement which may be used in a system of measuring ground movement.

Still further, it is an object of this invention to provide an anchoring arrangement comprising a series `of anchors within a drillhole designed to Iallow a tension carrying means to run unobstructed from each anchor to the opening of the hole.

These and other objects and features of the present invention will be apparent from the followingV description thereof wherein reference is made to the figures of the accompanying drawing.

FIG. l is a cut-away view of the explosive centerhole anchor revealing the several parts ,and the internal construction of the anchor.

FIG. 2 is a schematic View showing the anchor connected with an adapter to a pipe for placing the anchor within the drillhole.

FIG. 3 is a schematic view showing anchors in place within a drillhole with the connecting tension wires connected to ,a measuring unit at the surface of the drillhole.

Referring to FIG. 1 lof the drawing, 1 represents the centerhole anchor comprising a heavy walled center tube 2 which is made strong enough to be threaded without unduly weakening the tube. This tube may be constructed from seamless steel tubing, Ialthough welded tubing or tubing of `aluminum or other metal may also be used provided galvanic action is not a problem. Tube 2 is threaded on both ends 4 and 5. A small hole 6 is provided for attachrnent of the instrument connecting wire 21. A bushing 7 with outer corners rounded, which may be threaded or plain on the inside is tacked by Welding or brazing as shown at 8 to the center tube near end 4. The shorter outer tube 3 may be made of a thin deformable metal, for example, 5052-0 aluminum with a 0.065-inch wall thickness; though tubing or other material and Wall thickness can be used if it will withstand explosive expansion without fracturing. The end of tube 3 adjacent to end 4 of tube 2 is placed through a tightly iitting section of steel tube 9. The end of tube'3 is then crimped to form inner flange 10. Band 9 becomes tight during this crimping step and acts as a reinforcing band for ange 10. A cap 11 is made to seal tube 3 to tube 2 on the threaded portion of end 5 by welding at 13 flange 12, selected to lit over tube 2 to a section of tube 14 of the same thickness that band 9 was made of. A small hole 15 is drilled in cap 11 to pass detonator lead wires 25. The explosive 16 is a low energy detonating cord containing 5-10 grain per foot of PETN (pentaerythritetetranitrate), and the detonator 17 is a mild end primer. The mild end primer is attached to the detonating cord 16, and the opposite end is pinched to seal the explosive within the lead covering of the cord, then the primer is taped to the center tube with the lead wires 25 protruding through hole 15. The detnoatirig cord 16 is wound on the center tube 2. The amount of detnoating cord used will depend upon the explosive force desired and the grain strength of the cord, but in general from about to 40 inches of from about 5 10 grain cord will be used. The free end of the cord may be secured by taping to tube 2.

To assemble the anchor, the center tube 2 with the explosive attached is inserted in outer tube 3 so that bushing 7 seats against ange 10 of tube 3. A seal 18 of waterproof material such as permagum is placed at the juncture of bushing 7 and ange 10. A washer 19 is placed over protruding end 4 of center tube 2 followed by a nut 20 which is securely tightened. On the opposite end, the detonator lead wires are threaded through hole 15 in cap 11 and a coupling `agent 22, which may be a uid such as water or substances such as gels, waxes and fats etc., is added to ll the annulus between inner tube 2 and outer tube 3. Cap 11 is placed over outer tube 3 and a nut 23 is used to tighten the cap on the outer tube Permagum or like material such as used in seal 18 may be placed in the cap and on the threads between the cap and the nut to form waterproof seals 24. Rubber centering pads 35, four on each end, serve to center the anchor in the hole and prevent a rebound effect which causes poor adherence and comes about when the anchor is exploded ol center in the hole.

The thickness of the pads will be governed by the space between outer tube 3 and the wall of the drillhole 28 shown in FIG. 3. These pads may be cemented into place Awith a suitable cement and may be made with notches to render them more pliant.

FIG. 2 shows an explosive centerhole wire anchor 1 connected by an adapter 26 to a pipe 27. For insertion into a drillhole 23 (FIG, 3), any previously installed connecting wires 21 are threaded through opening 29v (FIG. 1) of inner pipe 2 of anchor 1. An additional connecting wire 21 as shown in FIG. 1 is attached to anchor 1 through hole 6. The anchor 1 is attached by a friction tit to adapter 26 and this connection is secured by tape to prevent separation during insertion. The other end of adapter 26 is fitted in pipe 27 and held secure by ring clamp 30. The detonator lead wires 25 are cut and spliced at 31 and then taped so that they will be insulated and waterproof. The lead wire hole 15 through cap 11 (FIG. 1) is sealed with a waterproof material. The anchor is then pushed to the desired depth within a drillhole and detonated. The detonation `causes a shock wave to radiate outward from the explosive charge. This wave is received by the coupling agent 22 which dampens the shock and transmits it to the outer tube 1 forcing it to expand the inside surface of the hole. A pull on pipe 27 then pulls the adapter 26 free from anchor 1 and separates the lead wires at the splice 31.

FIG. 3 shows an anchoring arrangement comprising a series of anchors 1 positioned in a drillhole 28. The connecting wires 21 are attached to measuring instrument 32 of the type described in the aforementioned copending application Ser. No. 438,796, which may be secured near the collar 33 of drillhole 28 by floating explosive rockbolts 34 of the type described in U.S. Patent 3,148,577 to Parsons.

The explosive centerhole anchoring arrangement has been described with reference to preferred embodiments but it is to be yunderstood that it is susceptible of changes in form and detail as dictated by its use. It may beconveniently used wherever it is desired to secure an immovable hollow tube within a solid. The inner tube may be adapted to receive, secure or position wires, tubes, pipes, bolts, shafts or poles etc., as will be readily apparent to those skilled in the art.

What is claimed is:

1. In a permanent anchoring arrangement for tensioned wire extensiometer means extending into a drillhole, the improvement comprising an explosive centerhole anchor having a heavy walled center tube, a tensioned wire means attached to said center tube, a shorter expandable larger diameter outer tube surrounding said center tube and sealed at its ends to form a watertight enclosure with the center tube, centering means exterior to and peripherally positioned near the ends of said outer tube, explosive means selectively positioned to occupy a `portion of said enclosure, a coupling agent occupying the remaining portion of said enclosure, and means to detonate said explosive means.

2. The anchoring arrangement of claim 1 wherein the arrangement comprises a series of said explosive centerhole anchors being permanently fixed at predetermined positions within said drillhole by detonation of the explosive within said anchors, the members of the series being arranged so that the wire means of the deeper anchors pass unobstructed through the centerholes of the shallower anchors and further extend to the collar of said drillhole.

3. The anchoring arrangement of claim 2 wherein the tensioned wires are connected to a linear-movement measuring device located near the collar of the hole, whereby ground movements may be detected and measured.

4. A method of permanently placing within. a drillhole having an opening on a ground surface, a series of explosive centerhole anchors carrying wires capable of being placed under tension, including a rst and subsequent explosive centerhole anchors, which comprises the steps of lowering said iirst anchor to a predetermined depth within the drillhole, securing said anchor to the walls of the drillhole `by remotely detonating the explosive contained within the anchor, passing `all wires attached to said rst anchor through the centerhole .of a second anchor, lowering said second anchor into said drillhole to a predetermined depth and spaced from said first anchor, securing the second anchor to the walls of the drillhole by remotely detonating the explosive contained therein, and repeating the process with subsequent anchors whereby all said tension wires are anchored within the drillhole at spaced intervals and pass unobstructed to the collar of said drillhole.

5. The method of claim 4 further comprising connecting the said wires to a linear movement measuring device whereby ground movements may be measured and detected.

References Cited UNITED STATES PATENTS 2,214,226 9/ 1940 'English 166-207 2,271,005 l/1942 Grebe 175-230 X 2,661,649 12/1953 Skinner 85--75 2,796,134 6/1957 Binkley 166-207 3,148,577 9/1964 Parsons 85-65 3,175,618 3/1965 Lang et al. 166--207 3,327,396 6/1967 Waddell 33--125 RICHARD C. QUEISSER, Primary Examiner.

I AMES H. WILLIAMSON, Assistant Examiner. 

